The present invention relates to a method of manufacturing spectacles presenting individualized progressive ophthalmic lenses.
In a number of prior art documentsxe2x80x94in this context exemplary reference is made to the German Patent DE-A-43 37 369, the trade journal DOZ August 1996, pages 44 to 46, the trade journal NOJ November 1997, from page 18 onwards, or the German Patent DE-A-197 01 312xe2x80x94it has been proposed to compute and manufacture individualized progressive ophthalmic lenses. This term is meant to be understood in the sense that the progressive area and/or an aspheric matching surface are individually computed in correspondence with the respective prescription data and other characteristics such as forward inclination, cornea/apex distance, etc.
An adaptation of the progressive ophthalmic lens to the spectacle frame or the frame shape is not considered in these prior art references.
Even though it is common to minimize the critical thickness of ophthalmic lensesxe2x80x94i.e. the center thickness in the case of lenses with a positive effect or the marginal thickness in the case of lenses with a negative effectxe2x80x94by an appropriate selection of the position of the prescription area, only the position of the two areas relative to each other is optimized exclusively for a minimization of the critical thickness, but not the shape of the prescription or adaptation area, respectively.
The present invention is based on the problem of providing a method of manufacturing spectacles comprising individualized ophthalmic lenses matched with the respectively chosen spectacle frame.
One inventive solution to this problem is defined in patent claim 1. Improvements of the invention are the subject matters of the dependent claims.
The inventive method of manufacturing spectacles with individualized progressive ophthalmic lenses adapted to the frame shape comprises the following steps:
Initially, the wearer of the glasses must select a spectacle frame he likes. The shape of the lens rings of this spectacle frame is detected with a precision better than +/xe2x88x920.5 mm in the x- and y-directions, i.e. in the direction of the frame plane (data set 1). This data set can be generated either by scanning the spectacle frame by means of a so-called tracer, or by detecting the shape of the spectacle frame by means of a scanner or an optical detector instrument, respectively, without contact. It is, of course, also possible to inquire the shape of the lens rings from the manufacturer of the respective spectacle frame and to incorporate the manufacturer""s data into the inventive method as well. In an alternative approach, the contour of the pattern disks can also be considered.
Moreover, the intersection points of the lines of sight through the plane of the lens rings is detected for at least two design distances of the progressive ophthalmic lenses with a precision better than +/xe2x88x921 mm (data set 2).
In a progressive ophthalmic lens designed for normal applications, the design distances are xe2x80x9cinfinitexe2x80x9d in one case and in the other case a close-range distance, e.g. 33 cm. With a progressive ophthalmic lens adapted for a particular application, other design distances may be present, of course; for spectacles adapted for computer monitor work, for example, the design distances were roughly 1 m in the first case and roughly 40 cm in the other case.
The detection of the intersection points for the respective design distances is known from prior art so that it need not be discussed in more details here.
These two steps of the method are known from prior art and are carried out by an ophthalmic optician as routine work when spectacles with progressive ophthalmic lenses are adapted to the wearer.
In distinction from the method so far adopted, the selection and positioning relative to the lens rings of a spherical or non-spherical surface is performed not only in view of the prescription data but also with application of the data sets 1 and 2, i.e. in consideration of the shape of the lens rings and the points of intersection of the lines of sight through the plane of the lens rings. In other terms, among xe2x80x9cblanksxe2x80x9d held in stock, for examplexe2x80x94i.e. blanks finished on one sidexe2x80x94that particular blank is selected that is best suitable not only with respect to the prescription data but also in view of the shape of the lens rings and the position of the points of intersection for the individually computed progressive ophthalmic lens.
Subsequently, a progressive area is computed with minimization of the critical thickness of the ophthalmic lens and with application of the data sets 1 to 3. The computation, i.e. the optimization of the progressive areaxe2x80x94starting out from an initial areaxe2x80x94may be carried out by conventional methods so that this step need not be discussed in more details here.
Then, the progressive area is manufactured and the ophthalmic lens is framed, using a semi-finished product finished on one side and without an edge, with application of the generated data sets.
It is a particular advantage when the area finished on one side is a spherical or non-spherical face area because this area can be better adapted to the course of the spectacle frame, specifically in the z-direction, i.e. in the direction orthogonal on the frame planexe2x80x94in distinction from the progressive area.
For this reason it is particularly preferred that the shape of the lens rings in the z-direction be determined, particularly with a precision better than +/xe2x88x920.5 mm. The shape of the lens rings is then also input into the data set 1.
Another improvement of the quality of the ophthalmic lens is achieved by the provision that the detection of the point of intersection of the lines of sight through the plane of the lens rings and the arrangement of the lens rings in front of the wearer""s eyes is detected with a precision better than +/xe2x88x920.5 mm in the x-, y- and z-directions.
It is particularly preferable that the shape of the face area and particularly the course be selected as a function of the shape of the lens rings. To this end, the face area may be a non-spherical area and particularly an area presenting two differently designed principal sections whose shape is selected as a function of the shape of the lens rings. In other terms, according to the invention a toric or non-toric area is used also when the prescription data does not require the use of a torus, so as to be able to achieve an optimum adaptation to the course of the lens rings. The astigmatism introduced by the torically or non-torically designed surface, which is actually undesirable, is then compensated by a corresponding surface astigmatism of the progressive area on the side of the eyes so that the total astigmatismxe2x80x94with consideration of the astigmatism of oblique bundles in the application positionxe2x80x94will correspond to the prescription values.
For the computation of the progressive lenses the following approach may be taken in particular:
In correspondence with prior art, the manufacturers of ophthalmic lenses use a product-dependent standard value of roughly 22 mm for the progression length L of continuous vision lenses.
For frames with a small disk height, some manufacturers offer special additional progression lengths shorter than the standard.
From prior art not any method is known that determines the progression length of a continuous vision lens in consideration of the cornea/apex distance (HSA) of the pre-adapted frame.
A standard progression length of 22 mm creates inexpedient effects as soon as the cornea/apex distance exceeds or drops below a defined mean value (15 mm) and hence the ophthalmic lens is no longer seated correctly in front of the point of rotation of the eyes in correspondence with an empirically determined position of use.
In accordance with the empirically determined position of use, an invariable progression length of 22 mm is the optimum only in the case of a mean HSA value of 15 mm. With smaller HSA values, the view must be lowered farther down while with a higher HSA value the point of reference in the near viewing range is reached with a slighter deflection of the line of sight already.
In correspondence with values gathered from experience, a lowering of the view relative to the horizontal deflection of the view by roughly 32 degrees occurs in reading. When the HSA in correspondence with the selected frame of the ultimate user is changed relative to the standard HSA value the deflection of the line of sight for achieving the full addition or for viewing through the point of reference in the near vision range BN does no longer correspond to the empirically determined position of use. This may enforce a posture of the head or deflection of the eyes, which may be troublesome for the wearer of the continuous vision lenses. With a smaller HSA value (e.g. 10 mm) the head or the eyes must be moved down (if this is possible at all) whilst with a higher HSA value (e.g. 20 mm) the head or the eyes must be raised in an unnatural manner.
In accordance with the present invention therefore a method is provided that is suitable to determine the optimum and individual progression length of the continuous vision lens by reference to the measured cornea/apex distance of a pre-adapted spectacle frame.
This problem is solved by the following steps:
(a) providing the value of the individual cornea/apex distance (HSA) of a pre-adapted spectacle frame,
(b) measuring the individual distance d between a point of reference in the distant vision range BF and a centering marker ZK,
(c) determining the optimum and individualized progression length (Lopt) in correspondence with the following formula:
Lopt=0.63*(HSA+13.5 mm)+d(BF, ZK).
The progression length so determined may be communicated to the lens manufacturer who produces then a continuous vision lens with this individualized progression length.